1. Field of the Invention
The present invention relates to a plastic fitting for plastic fluid tubing, and more particularly relates to a plastic fitting for plastic tubing having an internal split ring that grips onto the plastic tubing to prevent the plastic tubing from separating from the fitting.
2. Description of the Prior Art
Fluid fittings for plastic tubing are well known in the art. Additionally, plastic tubing fittings and plastic tubing are required in certain environments (for instance, semi-conductor manufacturing), wherein all fluid-handling components used in the manufacture of semi-conductors must be non-metallic, in order that the fluid-handling components would not react with semi-conductor manufacturing chemicals (e.g., various acids), resulting in deterioration of the fluid-handling components by the manufacturing chemicals.
U.S. Pat. No. 5,472,244 discloses various attempts to design plastic couplings for plastic tubing. Specifically, this patent teaches a concept of introducing a split ring into an internal annular recess formed in the cap nut. The split ring is designed to xe2x80x9cbitexe2x80x9d into a corresponding annular groove formed in the plastic tubing as the cap nut is screwed onto the main body of the coupling, in order to retain the plastic tubing in position on the plastic tubing coupling. Inasmuch as the split ring essentially totally circumscribes the plastic tubing, and specifically the annular groove in the plastic tubing, the sharp xe2x80x9cbitingxe2x80x9d edge of the split ring bites into the already weakened plastic tubing at the annular groove therein, further weakening the structural integrity of the plastic tubing as the cap nut and split ring are further tightened down upon the plastic tubing. This xe2x80x9cbitingxe2x80x9d of the sharp edge of the split ring into the plastic tubing can eventually cut through the plastic tubing, leaving nothing to retain the plastic tubing in fluid communication with the plastic coupling. This, of course, results in a leaking fluid connection and disengagement of the plastic tubing from the plastic coupling if the semi-conductor manufacturing chemical is under sufficient pressure.
It is therefore an object of the present invention to provide a plastic fluid fitting for plastic tubing that overcomes the problems inherent in prior plastic tubing fittings.
It is a further object of the present invention to provide a plastic tubing fitting of the type incorporating a split ring mechanism that grips onto the plastic tubing that retains the plastic tubing in functional position without cutting into the plastic tubing.
It is a still further object of the present invention to provide such a plastic tubing fitting that utilizes standard fluid fitting sizes in order to be utilized with standard flared tubing fittings.
It is a still further object of the present invention to provide such a plastic tubing fitting wherein radially inward force upon the plastic tubing to compress the tubing against a standard flared fitting is provided by a unique camming mechanism formed in the split ring and cap nut.
The present invention provides a plastic fitting for plastic tubing having a flared end (36). The plastic fitting comprises a main body (10) having a tip sleeve (16) at one end thereof and an externally threaded portion (14) at the other end thereof, a cylindrical cap nut (20, 52, 64) threadedly attachable to the main body (10) in a manner to compress the plastic tubing down against the tip sleeve (16) of the main body, and a resiliently deformable split ring (30, 42, 60) that resides within an annular internal recess (28, 50, 72) in the cap nut (20, 52, 64) for retaining the flared end (36) of the plastic tubing in position around the main body tip sleeve (16). The resiliently deformable split ring (30, 42, 60) includes a plurality of inwardly facing bosses (38, 46) that cooperate with respective spaced apertures (40) formed in the plastic tubing flared end (36). These split ring bosses (38, 46) engage the tubing flared end to retain the tubing flared end within the cap nut and in functional position around the main body tip sleeve (16).
In a first embodiment, the split ring (30) is simple in construction, having a rectangular cross-section, and is intended to reside within the internal annular recess (28) formed in the cap nut (20) in a manner that the bottom end of the cap nut annular recess (28) retains the split ring (30) in position within the cap nut (20), and the split ring inwardly facing bosses (38) retain the flared end (36) of the plastic tubing in position within the cap nut and positioned around the main body tip sleeve (16).
In a second embodiment, the split ring (42) is formed with a plurality of cam lobes (44) on the outer circumference thereof. These cam lobes (44) are designed to nest within respective detents (48) formed within the annular internal recess (50) formed in the cap nut (52). Alignment of the respective split ring cam lobes (44) and cap nut annular recess detents (48) permits the split ring (42) to be expanded slightly in order to be able to be positioned around the plastic tubing flared end (36) when the flared end is in position on the main body tip sleeve (16). Threadedly attaching the cap nut (64) to the plastic fitting main body (10) allows the respective split ring bosses (46) to engage respective spaced apertures (40) formed in the plastic tubing flared end, thereby permitting the split ring (42) to draw itself down around the plastic tubing flared end. This releases the cam lobes (44) from respective cap nut internal annular recessed detents (48), so that further rotation of the cap nut (64) onto the plastic fitting main body (10) causes the cap nut internal annular recess (50) to cam the respective cam lobes (44) toward the plastic tubing flared end in order to further tightly compress the split ring (42) down against the plastic tubing flared end and lock the split ring bosses (46) within the plastic tubing flared end spaced apertures (40) to retain the plastic tubing in position.
A third embodiment of the plastic fitting of the present invention incorporates the split ring cam lobes (62) and cap nut annular internal recess detents (82), and also incorporates angled annular front and rear surfaces (78, 80) of the split ring (60) and mating angular annular side walls (74, 76) of the recess (72) in the cap nut (64) in a design that enhances the ability of the cap nut (64) to compress the split ring (60) down upon the plastic tubing flared end, and also provides a mechanism for releasing the split ring (60) from the plastic tubing flared end as the cap nut is removed from the main body tip sleeve.